Ultrasound imaging systems typically include a hand-held module commonly referred to as a probe or scan head. The probe can include one or more transducer arrays that emit acoustic vibrations at ultrasonic frequencies, e.g., approximately 1 MHz to approximately 20 MHz or higher.
The probe can be held against a patient's body so that the acoustical energy is incident upon a target area on or within the body. A portion of the acoustical energy is reflected back toward the probe, which senses the return reflections, or echoes. The transducer array generates an electrical output representative of the return reflections.
The probe is usually connected to the base unit via a multi-conductor cable. The base unit contains the circuitry necessary to stimulate the transducer to generate acoustic output waves and amplify and process the resulting echoes. The base unit processes the reflected signal information into a form suitable for display as a visual image, and displays the image on a monitor.
The use of a cable between the probe and the base unit can have disadvantages. For example, the relatively thick cable can interfere with the dexterity of the user in manipulating the probe. Moreover, the cable can degrade the electrical characteristics of the probe. In particular, the cable adds capacitance to the interfacing circuitry in the probe and the base unit. This additional capacitance can decrease the signal to noise ratio in the signals being transmitted through the cable. Also, the cable needs to be sterilized, or covered in a sheath that acts as a sterile barrier when the probe is used in a sterile environment, thus adding to the time and effort required to prepare the ultrasound imaging system for use.
The above-noted disadvantages of wired probes can be alleviated or eliminated through the use of a wireless probe, i.e., a probe that transmits information to the base unit by wireless means such as radio frequency (RF) signals. To facilitate wireless operation, a probe requires circuitry suitable to generate acoustic output waves and amplify and process the reflected acoustic echoes into a form suitable for sending over a wireless link.
A wireless probe needs to be equipped with a battery or other suitable power source. In applications where the probe is to be used in connection with a critical medical procedure, the service life of the battery, or the minimum interval between recharging, should be greater than the duration of the procedure. Ideally, the service life or recharging interval is substantially longer than the duration of a single procedure, so that the battery can be used throughout multiple procedures without being replaced or recharged.
The use of a battery can give rise to other needs unique to a battery-powered probe. For example, it may be necessary to monitor the charge state of the battery on a real-time basis, to ensure that that sufficient charge is left to perform a critical medical procedure.
Moreover, the probe and its battery may be equipped with electrical contacts to establish contact between the probe and a removable battery, or to facilitate charging of a non-removable battery. Because the probe may be exposed to electrically-conductive fluids, such as water or ultrasound coupling gel, the contacts on the probe need to be isolated from each other to prevent the unintended flow of electrical current therebetween. A need likewise exists to isolate the contacts on the battery from each other. Also, the probe should be sealed to prevent fluids from infiltrating into the interior of the probe and potentially damaging the electronic components housed within the probe.
Eliminating a cable between the probe and the base unit is believed to increase the potential for the probe to be accidentally dropped. A wireless probe therefore needs to be configured to withstand the mechanical shocks induced by impacts. One possible technique for providing impact resistance is potting the various electronic components within the probe. Potting, however, can prevent the servicing and re-use of the components. A need therefore exists to provide a wireless probe with impact resistance, while maintaining the capability to service or re-use the electronic components of the probe.